Modern ink jet printers may produce photographic-quality images. A thermal ink jet printer includes a number of nozzles spatially positioned in a printer cartridge. Ink is heated when an electrical pulse energizes the resistive element forming the thermal resistor. The ink resting above the thermal resistor is ejected through the nozzle towards a printing medium, such as an underlying sheet of paper as a result of the applied electrical pulse.
This thermal resistor is formed as a thin film resistive material disposed on a semiconductor substrate and a dielectric layer as part of a semiconductor chip. Several thin film layers are formed on the semiconductor chip, including the dielectric layer above the substrate, the resistive layer forming the thermal resistor above the dielectric layer, and an electrode layer that defines the electrodes coupled to the resistive layer to which the pulse is applied to heat the thermal resistor and vaporize the ink. At least one dielectric layer, and a protection layer are typically above the electrode layer. The protection layer protects the resistive layer and other layers from oxidation and chemical degradation caused by the ink as it is heated and ejected from the nozzle. Example dielectric layers include silicon nitride and silicon carbide layers.
Many thermal ink jet printheads use a tantalum/aluminum (TaAl) (various other resistor materials are possible like tantalum silicon nitride (TaSiN)) thin film as the resistive layer. Over time, this TaAl layer may degrade as numerous electrical pulses are applied during printing. It has been found that these thermal resistors often start failing at the grounded edge due to voids induced by electromigration. Also, the gradual electric charging of the dielectric layers over the electrode and thermal resistors may lead to potential build up sufficient to discharge the charges by arcing to ground and result in rupture of the resistors. It has also been observed that some thermal resistors had different failure lifetimes depending on the configuration of the electrode layer relative to the thermal resistor, and the amount of compressive or tensile forces applied by the dielectric layers over the electrode layer.